In order to install threaded fasteners, such as screws, bolts, nuts or the like, a torque tool is utilized to apply the necessary torque. Various types of torque tools are available, including wrenches, screwdrivers and other power tools, for engaging the threaded fastener and rotatably advancing the threaded fastener by the application of torque thereto. As such, torque tools permit threaded fasteners to be installed in a wide variety of workpieces, including the threaded fasteners installed during the assembly of an aircraft, an automobile and a wide variety of other structures.
In installing a threaded fastener, it is generally desired to tighten the threaded fastener until the threaded fastener is appropriately stretched or tensioned, thereby insuring that the threaded fastener securely engages the workpiece(s) in which the fastener is installed. In this regard, the desired tension in the fastener may be determined in advance by a design engineer to ensure that the structure is appropriately secured by the threaded fasteners. However, it is difficult to directly determine the tension in an installed fastener. In this regard, although the tension could be readily calculated if the variation in the length of the installed fastener from the nominal length of the fastener could be determined, the length of most installed fasteners cannot be readily measured.
As such, the torque applied to the threaded fastener is more commonly specified and measured since the tension in the fastener can be estimated based upon the applied torque. In installing threaded fasteners, it is therefore desirable to threadably insert a fastener until the desired torque has been applied to the fastener since completing the installation of a fastener without applying sufficient torque may not adequately fasten the workpiece(s). Conversely, applying excessive torque during the installation of a fastener may damage the workpiece(s). As such, handheld power tools may be configured to install a fastener with a predetermined amount of torque.
For example, pneumatic and hydraulic power tools are available that have a target torque setting. As such, these power tools will install a threaded fastener with the application of the target torque. However, pneumatic and hydraulic power tools having a target torque setting cannot be re-configured in the field or along the assembly line to have a different target torque setting. Instead, the pneumatic and hydraulic power tools must be returned to a calibration laboratory in order to change the target torque setting. Since many assembly processes require different fasteners to be installed to different levels of torque, one solution is to provide a multiplicity of torque tools with each tool configured to install threaded fasteners to a different level of torque. Alternatively, a single torque tool may be utilized, but the torque tool must be repeatedly returned to the calibration laboratory in order to be reset to have different target torque settings, as required by the assembly operation. Each of these approaches has disadvantages, however, in that the use of multiple torque tools requires the purchase and maintenance of additional torque tools which, in turn, increases the overall capital and operational costs of the assembly process. In addition, the repeated recalibration of a single torque tool to multiple target torque settings decreases the overall efficiency of the assembly process, since the torque tool must be repeatedly taken off line for some period of time to re-calibrate the torque tool. Moreover, pneumatic and hydraulic power tools must disadvantageously remain tethered to a pneumatic or hydraulic power supply.
Handheld power tools designed to apply torque to threaded fasteners are also available that are powered by alternating current (AC). In this regard, AC torque tools have been developed that include a number of preset target torque settings. As such, an operator can push an appropriate button on the user interface of the AC torque tool in order to select an appropriate target torque setting prior to installing threaded fasteners to the selected target torque value. However, these AC torque tools are generally quite large and expensive tools and, as a result, are not widely utilized. Moreover, AC power tools also must disadvantageously remain electrically connected to an AC power supply.
Accordingly, it would be desirable to provide a torque tool that permits the operator to readily select the target torque settings such that a single torque tool could be utilized to apply various levels of torque to threaded fasteners without having to return to a calibration laboratory or otherwise remove the torque tool from service. Additionally, it would be advantageous to provide a torque tool that was readily portable and was not tethered to a stationary power supply, such a pneumatic or hydraulic power supply or an AC power line, as required by conventional torque tools.